1. Field of the Invention
The present invention relates to an optical signal transmission device that makes use of both optical time division multiplexing (OTDM) Carrier Suppressed—Return to Zero (CS-RZ) signals and four wave mixing induced by Optical phase conjugation (OPC).
2. Description of the Related Art
To transmit an optical time division multiplexing (OTDM) signal at a 1.55-μm band in a standard single mode fiber (SSMF) with a zero-dispersion at a 1.3 μm band, the wavelength and nonlinearity in the fiber must be compensated. As one method for compensating for the wavelength dependence in the fiber, a method that uses dispersion compensated fiber arranged after transmission fiber is known (A. D. Ellis and D. M. Spirit, “Unrepeatered transmission over 80 km standard fiber at 40 Gbit/s,” IEE Electron. Lett., 1994, 30, (1), pp. 72–74). Further, as a method to compensate for the wavelength dependence (chromatic dispersion) in the fiber, optical phase conjugation (OPC) is known (A. Yariv, D. Fekete, and D. M. Pepper, “Compensation for channel dispersion by nonlinear optical phase conjugator (OPC),” OSA Opt. Lett., 1979, 4, (2), pp. 52–54; S. Watanabe, T. Naito, and T. Chikama, “Compensation of chromatic dispersion a single-mode fiber by optical phase conjugation,” IEEE Photon. Technol. Lett., 1993, 5, (1), p. 92–95; R. M. Jepson, A. H. Gnauck and R. M. Derosier, “Compensation of fiber chromatic dispersion by spectral inversion,” IEE Electron. Lett., 1993, 29, (7), p. 576–578; M. C. Tatham, G. Sherlock, and L. D. Westbrook, “Compensation fiber chromatic dispersion by optical phase conjugation in a semiconductor laser amplifier,” IEE Electron. Lett., 1993, 29, (21), pp. 1851–1852).
The concept of dispersion compensation using OPC was first proposed by Yariv et al. in 1978 (A. Yariv, D. Fekete, and D. M. Pepper, “Compensation for channel dispersion by nonlinear optical phase conjugator,” OSA Opt. Lett., 1979, 4, (2), pp. 52–54). In this technique, an optical phase conjugator is arranged at the mid point of the transmission route. A signal, the quality of which becomes worse due to wavelength dispersion in the fiber, is received by the optical phase conjugator, and the optical phase conjugator emits a phase conjugate signal, the frequency of which is inverted as compared to the original signal. One characteristic of dispersion compensation using OPC is that it does not require a complicated design.
Optical transmission devices employing OPC have been reported (S. Watanabe, T. Naito, and T. Chikama, “Compensation of chromatic dispersion a single mode fiber by optical phase conjugation,” IEEE Photon. Technol. Lett., 1993, 5, (1), p. 92–95; R. M. Jopson, A. H. Gnauck and R. M. Derosier, “Compensation of fiber chromatic dispersion by spectral inversion,” IEE Electron. Lett., 1993, 29, (7), p. 576–578; M. C. Tatham, G. Sherlock, and L. D. Westbrook, “Compensation fiber chromatic dispersion by optical phase conjugation in a semiconductor laser amplifier,” IEE Electron. Lett., 1993, 29, (21), pp. 1851–1852). OPC may classified into two categories based on the media used by the device to generate phase conjugated light. In one category, the device uses optical fiber (S. Watanabe, T. Naito, and T. Chikama, “Compensation of chromatic dispersion a single-mode fiber by optical phase conjugation,” IEEE Photon. Technol. Lett., 1993, 5, (1), p. 92–95; R. M. Jopson, A. H. Gnauck and R. M. Derosier, “Compensation of fiber chromatic dispersion by spectral inversion,” IEE Electron. Lett., 1993, 29, (7), p. 576–578). In the other category the device uses a semiconductor optical amplifier (SOA) (M. C. Tatham, G. Sherlock, and L. D. Westbrook, “Compensation fiber chromatic dispersion by optical phase conjugation in a semiconductor laser amplifier,” IEE Electron. Lett., 1993, 29, (21), pp. 1851–1852). Both of these devices make use of Four Wave Mixing (FWM) induced in the nonlinear media.
An optical signal transmission device, wherein a 80 Gbit/s OTDM signal is transmitted over 106 km SSMF using a 1.2 ps optical pulse, is reported by Feiste et al. (U. Feiste, R. Ludwig, C. Schmidt, E. Dietrich, S. Diez, H. J. Ehrke, E. Patzak, H. G. Weber, and T. Merker, “80-Gb/s transmission over 106-km standard-fiber using optical phase conjugation in a Sagnac-interferometer,” IEEE Photon. Technol. Lett., 1999, 11, (8), pp.1063–1065).